Pipe-lines are routed through remote areas to transport their product to the market. Shut-off or "block" valves are located along the way, as needed for safety and rerouting efficiency and without particular regard to accessibility for operation and maintenance. While a block valve may be located at a convenient operating station, it is more likely not to be so placed. Pipe-lines are sized to permit the flow of massive volumes of product with minimal pressure losses and the block valves are consequently large, heavy assemblies which require power for opening and closing. Hydraulic or pneumatic driven actuators are preferred for reasons of simplicity and efficiency. Either a straight gas, or a gas over oil system is used with the operation controlled by a small four-way valve. With an appropriate pipe-line product and sufficient working pressure, the pipe-line itself can be the power source, but this is only possible when the product is a gas within acceptable contamination limits and environmentally tolerable. Fortunately, block valve operation is not a frequent event, so that high pressure nitrogen "bottles" placed on location as a power source can serve for an extended period with no attention other than scheduled inspections. Furthermore, bottled nitrogen is inexpensive and is readily available in all parts of the world.
The bottled gas pressure is in the 2,500 to 3,000 psi range when freshly charged, and obviously, with this limited volume available, a leak is a potential maintenance and reliability problem. As a general rule, leakage and internal clearances for reliable operation are necessary companions, so that all otherwise suitable four-way control valves have an inherent degree of leakage in the neutral mode. Therefore, it has been a common practice to place a two-way cut-off valve between the pressure supply and the four-way valve with both being pilot or solenoid operated for control at remote locations. The added costs, circuit complexity and maintenance are tolerated as necessary "trade-offs".
Metal-to-metal sealing of high pressure gases is routine using needle valves, where the valve seating force is simply increased until cut-off is achieved, but pilot and solenoid valve operators lack such capability. Some smaller sized pilot operated cut-off valves have enjoyed limited success using deformable poppets, made from nylon or a similar material, in conjunction with a metallic seat, but this arrangement is not suitable for use in the larger valves because of the scale effect. In time, the deformable material of the poppet takes a permanent set and behaves much like a metal-to-metal contact seal. Conventional resilient sealing elements such as "O" rings can be displaced by fluid flow or high pressure and are generally unreliable for such service. While it is recognized that "deformable" and "resilient" are somewhat ambiguous terms related to elasticity, in the context of this application, "deformable" infers an independent ability to maintain functional shape while "resilient" infers a shape dependent on external support. Kepner, in his U.S. Pat. Nos. 2,959,188 and 3,335,750, teaches a poppet type check valve seat/seal design wherein the seat combines metallic and resilient elements arranged to contact the poppet for reliable, non-leaking operation. These poppet valves, available from Kepner Products Co., Inc. in a pilot operated configuration as their "2700 Series", have been widely used as cutoff valves for block valve actuators since the late 1970's.
Others, notably Acar, U.S. Pat. No. 4,109,675; Boehringer, U.S. Pat. No. 4,172,469 and Nimberger, U. S. Pat. No. 4,655,251, have taught poppet check valve designs using a combination of metallic and resilient seat elements for non-leaking operation.
Still others, for example Pick, U. S. Pat. No. 2,240,163, have taught the use of poppet valves in four-way configurations with either deformable poppets or poppet seals working against metallic seats, and such devices continue to be the common commercial practice. A poppet type control valve can have greater tolerance for unfiltered grit in the operating medium than an equivalent spool type valve and, all things being equal, is preferred for reliability in critical applications.
The object of the present invention is therefore, to provide a poppet type directional control valve for reliable, non-leaking gas operation in pipeline service and other critical applications, and thus, to eliminate the need for an auxiliary cut-off valve and the attendant cost, circuit complexity and maintenance requirements involved.
The present invention accomplishes this objective by incorporating a combination metallic and resilient multiple part seat in a poppet type four-way control valve which thereby differs from conventional metallic seat practice. Such seats have been known for many years and poppet unseating pilot plungers are well known in pilot operated relief and check valve design. The inventor has first recognized that assembly of the metallic/resilient seat in a valve body cam be facilitated by the use of a separate unseating pilot plunger, while the pilot plunger can also include the exhaust valve means required for a directional control function, so as to provide the long needed non-leaking directional control valve.